It is known to provide printhead circuits for printers such as inkjet printers. For example, the inkjet industry has been working on how to drive piezoelectric printhead actuators for more than fifty years. Multiple drive methods have been produced and there are multiple different types in use today, some are briefly discussed now.
Hot Switch: This is the class of driving methods in which the generation of drive waveforms for the actuators takes place within the print head itself. Typically, the electronics in the print head are implemented in an integrated circuit (ASIC). In this approach, all of the power dissipation associated with generating the waveforms and connecting them to the actuators (a total of 0.5 CV2 per driven actuator) occurs in the print head. This was the original drive method, before cold switch became popular.
Cold Switch: This describes an alternative structure using a Common Drive Waveform (CDW). in which the electronics that generate the CDW is located outside of the print head. The electronics within the print head (typically an ASIC) is then only required to provide multiplexer functionality to connect this externally generated CDW to the appropriate actuator nozzles. A key advantage of this approach is that a significant proportion, in some cases perhaps around 80%, of the 0.5 CV2 energy dissipation occurs in the external waveform generation electronics and, consequently, the dissipation in the print head and the ASIC is reduced. This makes it much easier to maintain the print head at or around a suitable operating temperature.
However, for printed image quality reasons, it is highly desirable to provide a mechanism for trimming the drop velocity or drop volume on a per actuator nozzle basis. This requires that the drive circuits are capable of generating an individually-tailored waveform to each actuator nozzle. In a hot switching environment, in which the waveforms are generated in the print head itself (typically in an ASIC) this is straightforward to achieve. In a cold switching environment, however, where a common drive waveform (CDW) is generated outside of the print head, the modification of the waveform on a per actuator nozzle basis is more difficult to achieve.
US 2005200639 shows a printer with drive circuitry for actuators using a common drive waveform applied to one side of the actuators and with switches for coupling the other side of the actuators to a common return path. The switches are controlled to switch on sloping edges of pulses of the common drive waveform to adjust a height of the pulses, for an array of actuators. Adjustments can be made for each printed line so that blocks can be varied around an average weighting.
U.S. Pat. No. 8,303,067 shows a stepped common drive waveform with multiple different pulses having multiple levels, switching is carried out to select which of the different pulses to use to generate different sizes of droplet. There is adjustment of ejection speed by widening or narrowing intervals between successive droplets.
US 2009/0278877 shows common drive waveforms A and B with multiple levels, with adjustment of h1, a hold time when the chamber is at maximum volume before contraction and ejection.
US 2011/0128317 shows a common drive waveform and adjustment of timing of gating during a ramp so as to change a height of the ramp.
US20120262512 shows a common drive waveform and shows changing a height of part of a pulse by controlling a timing of a switch to couple the common drive waveform to an actuator, to compensate for variations between different actuators.